(a) Field of the Invention
The present invention relates to an automatic transmission for a vehicle and more particularly to a planetary gear train of an automatic transmission for a vehicle that minimizes complexity, realizing at least nine forward speeds and at least one reverse speed improves power delivery performance and fuel consumption by multi-stages of an automatic transmission, and improves driving stability of a vehicle by utilizing a low rotation speed of an engine.
(b) Description of the Related Art
Generally, in the field of an automatic transmission, multiplicity greater number of shift-stages provides technology for enhancement of fuel consumption and drivability of a vehicle. In particular, increases to the cost of oil had resulted in requirements to enhance fuel consumption of a vehicle. In other words, research for an engine has conducted to achieve weight reduction and to enhance fuel consumption. For example, research on an automatic transmission has been conducted to simultaneously improve drivability and fuel consumption by inclusion of additional shift stages.
For example, to achieve more shift-stages for an automatic transmission, the number of components is typically increased, which may deteriorate installability, production cost, weight and/or power flow efficiency. Therefore, to maximally enhance fuel consumption of an automatic transmission having more shift-stages, improved efficiency must include a smaller number of components.
Recently, an eight-speed automatic transmission has been introduced and a planetary gear train for an automatic transmission enabling more shift-stages is continuously required. An automatic transmission of eight or more shift-stages typically includes three to four planetary gear sets and five to six control elements (e.g., frictional elements). In other words, the total length may be increased and may produce a deterioration of installability. For example, disposing planetary gear sets in parallel or employing dog clutches instead of wet-type control elements has been attempted. However, such an arrangement may not be widely applicable, and using dog clutches may deteriorate shift-feel.
The above information disclosed in this section is merely for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.